Biological control of cocoa black pod disease by fungi agents : arbuscular mycorrhizal fungi and Trichoderma asperellum

AMF and Trichoderma sp. can be used as an alternative to:

Øreduce chemical pesticides for cocoa tree protection and nutrition against P. megakarya;

Øproduce safety and healthy plants in nursery;

Øimprove cocoa pot nutritional quality (high amino acid content)

Cocoa black pod rot, caused by Phytophthora megakarya, causes substantial yield losses worldwide, particularly in Africa. In optimum conditions, Losses can reach 80 % . Chemical control mostly used is expensive and environmental harmful. An alternative is the use of biological control agent such as Arbuscular mycorrhizal Fungi (AMF) and Trichoderma (Ngonkeu et Nwaga, 1998; Tondjé etal., 2007). Both microorganisms are know to improve protection against plant telluric pathogens and reduce inorganic fertilizer input up to 70 % (Ngonkeu, 2009). The goal of this work is to assess dual inoculation of Arbuscular mycorrhizal Fungi (AMF) and Trichoderma asperellum on the growth and the biological control of cocoa black pod diseases due to P. megakarya. In the present work, we are focusing on biochemical compound in plant fungi interactions. Specifically the role of phenolic compound and amino acids in AMF and Trichodermaassociations is discussed.

Table 1. Effect of AMF and T. asperellum on some agronomical and physiological parameters of cocoa tree,

18 weeks after seedling

a b c c c d 0 2 4 6 8 10 12 14 T0M0 T0M1 T0M2 T M0 T M1 T M2 P h os ph oru s c onte nt (mg /100 g of p lant ) 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 0,18 0,2 Ac ids pho s phat as es (µm ol/m in/m g of Prot) Phosphorus (mg/100g of plant) Acid phosphatases (µmol/min/mg of prot,)

b b c bc c a a a b b c c 0 10 20 30 40 50 60 70 80 T0M0 T0M1 T0M2 T M0 T M1 T M2 Traitments S ymp to m s coring ( x1 0) an d r oot c o lo ni z ati on (% )

Symtom scoring (x10) Root colonization (%)

Fig 2. Effect of AMF and T. asperellum on symptom scoring of cocoa black pod disease, 18 weeks after seedling

Fig 3. Effect of AMF and T. asperellum on healthy and inoculated leaf on soluble amino acids and phenols of cocoa tree pod disease, 18 weeks after

seedling 48.4a 6.0bc 8.0a 22.9a 44.6a 20.0b TM2 46.5a 3.8bc 7.6a 16.7b 44.0a 26.7b TM₁ 46.4a 4.0bc 8.9a 16.5b 41.6a 0.0c TM₀ 50.0a 7.1a 7.1a 17.3b 37.0b 51.7a T₀M₂ 46.5a 4.0bc 7.13a 22.8a 37.0b 50.7a T0M1 37.2b 2.6c 2.9b 9.8c 24.6c 0.0c T₀M₀ Chlorophyll rate (%) Dry matter (g.plant-1₎ Fresh root (g.plant-1₎ Leafs number Height (cm) Root colonization (%) Treatments b cd bc a a d bc d cd a b e 0 10 20 30 40 50 60 T0M0 T0M1 T0M2 T M0 T M1 T M2 Treatments Ami no acids (µ g/g) 0 1 2 3 4 5 6 Phen ols c on tent (mg/ g)

Healthy (aa) Inoculated (aa) Healthy (phenols) Inoculated (Phenols)

Fig 1. Effect of AMF and T. asperellum on P and acids phosphatases cocoa tree, 18 weeks after seedling

MATERIAL AND METHODS

RESULTS AND DISCUSSION

CONCLUSION

Height, leafs number, fresh root, dry matter, root colonisation and symptom scoring

Means parameters evaluated, 18 weeks after seedling Agronomical Physiological Biochemistry

Chlorophyll rate and P Content Acids phosphatases, soluble amino acids and phenolic compound

AMF and T. asperellumincrease significantly (P=0.001) leaf amino acids content (1.6 to 2.7 fold). There is positive correlation between root colonization and amino acids content (P = 0.0002 ; r2 _{= 0,812); and}

negative correlation between symptom scoring and amino acids (P= 0.015; r2

=-0.61).

Leaf Phenolic compound increase (1.7 to 2.5 fold) after inoculation by AMF and T. asperellum. Positive correlation have been observed between root colonization and phenolic content (P<0.001 ; r2 _{= 0.866)}

and negative correlation between symptom scoring and amino acids (P = 0.002 ; r2

=-0.716).

Amino acids and phenolic compound synthesis combined to P nutrition are potential mechanisms used by these biological control agents for plant protection. Sterilized soil substratum

ToM1 ToM2 TMo TM1 TM2

4 x 5 pots EXPERIMENTAL DESIGN ToMo

a b

a: Gigaspora margarita b: Trichoderma asperellum

c d

c: Phytophthora megakarya

d: Leafs inoculated and incubation method

AMF and Trichoderma asperellum increased significantly (P=0.01) plant height (1,5 to 1.8 fold), fresh root (2.4 to 3 fold), dry matter (1.5 to 2.3 fold) and chlorophyll rate (1.25 to 1.3 fold). Interaction AMF-T. asperellumis not significant at P=0.01.

P uptake increase significantly (P=0.001) after inoculation with AMF and Trichoderma (2 to 3.5 fold). The interaction AMF-T. asperellum is positive and significant (P=0.001). These results can be related to acids phosphatases stimulation in plant root; responsible to P-organic matter hydrolyzation (Tchameni et al., 2009).

AMF and T. asperellum reduce significantly (P = 0.001)

P.

megakarya

BIOLOGICAL CONTROL OF COCOA BLACK POD DISEASE BY FUNGI AGENTS:

ARBUSCULAR MYCORRHIZAL FUNGI AND TRICHODERMA ASPERELLUM

Tchameni1_{N.S., Nana Wakam}1_{L., Owona}2_{A., Fokom}1_{R., Tchana}2_{T., Mbarga}2_{J.B., Sime}1_{A. Tsagué}1_{M., Ten Hoopen}2_{M., Kosma}1_P.,

Meboma2_{M.E., Nyem}2_{E, Hoopen}2_{T.M., Kuaté}2_{J., Tondjé}2_{P.R., Etoa}1_{F.X., Ongéné N.A. and Ngonkeu}2_{* M.E.L}

1: University of Yaoundé I P.O. Box 812 Yaoundé Cameroon

2: Biological Control and Applied Microbiology Laboratory, IRAD Cameroon P.O. Box 2027 Yaoundé Cameroon

* Corresponding author: [email protected]

REFERENCES

1- Ngonkeu et Nwaga, 1998. Cam.J. Biol. Biochem. Sci

8(1): 56-67

2- Ngonkeu, 2009. Thèse de Doctorat Ph.D. Université de Yaoundé I. 215p

3- Tchameni N.S., Nana wakam L., Jemo M., Fokom R.,

Thé C. and Nwaga D., 2009. Res. J. Agric. & Biol. Sci.,

5(4):480-488.

4- Tondje P.R., Roberts D.P., Bon M.C., Widmer T., Samuels G.J., Ismaiel A., Begoude B.A.D., Tchana T., Nyemb-Tshomb E., Ndoumbe-Nkeng M., Bateman R., Fontem D. and Hebbar K.P., 2007. Biological Control 43: 202–212.

INTRODUCTION

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